BACKGROUND. Through a RNAi synthetic lethal screen we have identified the protein SUMOylation pathway to be required for the viability and transformation of Ras mutant cancer cells. PURPOSE. In this project we aim to address the following questions: 1) the mechanism by which inhibition of SUMO ligases is synthetically lethal with the KRAS oncogene; 2) which cellular proteins are differentially SUMOylated in Ras mutant cells; and 3) How the changes in SUMOylation status of these proteins affect their function in the context of Ras mutant tumors. SIGNIFICANT MATERIALS AND METHODS. 1) shRNAs that target the SUMO E1 and E2 ligases and SUMO pathway proteins; 2) Stable cell lines expressing SUMO proteins and ligases; 3) mass-spectrometry methodology for identifying SUMOylated proteins in cell lysates. FY2015 ACCOMPLISHMENT. We discovered that KRAS mutant colorectal cancer cells exhibit altered patterns of protein SUMOylation and Ras driven transformation requires SUMO ligase activity. This study was published in 2015.